A numerical controller successively pre-reads blocks of a plurality of NC programs from a memory or from a storage device connected via a network, while executing the NC programs in parallel. The execution times of the pre-read blocks are integrated in respect of all of the NC programs that are the object of pre-reading, and when an NC program having the shortest integrated execution time of the pre-read blocks can be pre-read, the next block in that NC program is pre-read. On the other hand, when that NC program cannot be pre-read, the NC program is excluded from the pre-reading objects.